This invention relates to solder dispensing devices for use in electronic component assembly, and more particularly, to a new and improved solder dispensing device and method of operation, the device being of the type having a recharageable battery power supply for energizing an electric solder feed motor and having a unique dispensing extension tip and a solder spool reloading mechanism.
In the field of electronic assembly, soldering of electronic components is a major concern in establishing continuous electrical contact for providing a pathway for signal transmission. An example of where this problem exists is in the computer industry. Large computers include a plurality of printed circuit boards which require literally hundreds of delicate coaxial cable connectors to be soldered thereto. Computer equipment is a good example because it is often necessary to solder joints which are located several centimeters beneath a layer of delicate coaxial conductors.
The procedure of holding metalic solder in one hand while applying heat with a soldering tool with the other hand is difficult because of the lack of accessibility to the designated solder joint. A further difficulty involves the inabilty to maneuver the hand holding the solder around the many delicate coaxial conductors attached to the printed circuit board. If the hand-held method is employed, a long piece of solder must be extended by several inches to reach the solder joint. Under these conditions, a measurable amount of the solder is left unsupported and usually bends or curves due to the soft characteristics of the solder alloy. The unsupported solder thus becomes unstable and often results in the inability to deposit the solder at a particularly soldering joint location on the printed circuit board.
It is common in the computer industry to employ a coaxial conductor connector at the end of a coaxial conductor wherein the coaxial conductor connector is utilized for connecting the coaxial conductor to the printed circuit board. The coaxial connector is designed to receive and seal a coaxial conductor from the rear side of the connector. The coaxial conductor comprises a structure commonly known in the industry which includes a bare conducter wire at the center of the cable which is separated from a concentric braided conductor by a layer of electrical insulation. Further, the braided conductor may be enclosed by yet another layer of insulation forming the exterior of the coaxial conductor.
The braided conductor is then electrically connected to the body of the coaxial connector so that the connector becomes an extension of the braided conducter. The layer of insulation surrounding the bare center conductor wire is then passed through a hooded body portion of the coaxial connector with the center conductor wire extending therefrom for connection to the proper location on the printed circut board. The coaxial connector body portion also includes a plurality of four connector legs extending therefrom for inserting into preformed penetrations within the printed circuit board. It is these preformed penetrations with the connector legs inserted therein, that must be completely filled with solder for insuring maximal signal transfer.
An acceptable soldering technique to be utilized on double sided printed circuit boards is to apply a source of heat from a soldering iron on one side and a supply of solder on the opposite side of the printed circuit board. The iron on one side and a supply of solder on the opposite side of the printed circuit board. This technique is practiced to ensure that the connector body of the coaxial conductor is completely soldered to the solder pads of the printed circuit board for providing maximum electrical transfer through the cable. The solder pad is generally a metallic section located on the printed circuit board which is utilized for making contact with the coaxial connector body.
The legs extending from the body of the connector are inserted into the preformed holes in the printed circuit board during assembly of the circuitry. Next, the solder supply is applied to the solder pad of the side of the printed circuit board which is to be electrically connected while the source of heat is applied to the opposite end of the preformed hole on the other side of the printed circuit board. Because the connector body is comprised of metal and is an extension other side of the printed circuit board. Because the connector body is comprised of metal and is an extension of the braided conductor, the solder will deposit on the connector body and on the connector legs filling the preformed holes through the printed circuit board. This soldering method ensures clean and electrically continuous solder joints.
Because the printed circuit boards employed in computer equipment can be, for example, approximately three feet wide and three feet long, hundreds of coaxial cables are distributed across the board. During the assembly of the board or during the repair of any particular circuit connected to the board, a cable located deep within the nest of wires is difficult to reach. Thus, a major problem that exists in the computer industry is that of accessing a particular solder joint and expelling a measured amount of solder to the solder joint while supporting and maneuvering the length of solder through a maze of obstructions. An equally vexing problem is that of avoiding direct overheating damage to the insulation of signal wire and completing the application of the solder to a joint within a time limitation for avoiding heat damage to delicate coaxial conductor insulation by heat transfer.
In repair situations which require the removal of a coaxial connector from the printed circuit board, a desoldering tool has been employed for removing the solder from the heated side of the soldering joint. However, upon resoldering the electrical connections in the repaired circuit, the same problems exist that were associated with the original assembly and wiring of the printed circuit board. Under these conditions, it is very difficult to maneuver the melted solder up the leg of the connector body and into the preformed holes of printed circuit body fast enough to avoid causing temperature damage to the delicate installation about the coaxial cable.
The soldering procedure of applying heat to one side of the printed circuit board and the solder to the opposite side is necessary for the following reasons. First, a sufficient amount of solder must be deposited on the body of the coaxial connector and within the upper and lower legs extending from the connector for ensuring maximum signal transfer through the coaxial cable. Next, a solder heating iron cannot be safely placed between the coaxial cables extending from the bodies of the connectors because of potential damage to the cable installation from the hot soldering iron. Finally, the heating cycle time for completing an actual soldering joint is extremely critical because the delicate coaxial conducter installation will not tolerate the extended time necessary for the molten solder to flow through the preformed holes in the printed circuit board if soldering was completely conducted from only one side of the board. Thus, if both the source of the heat and the solder were applied from the same side of the printed circuit board, an extended time would be required to direct the heated solder from the lower legs of the connector through the board and to deposit a sufficient amount of molten solder on the connector body to produce an acceptable soldered joint.
It has been found that completing the soldering task from a single side of the printed circuit board, for example, the side that the soldering iron is located on, permits soldering the lower parts of the legs extending from the conductor body. However, this technique was not acceptable because the entire connector body, which is an extension of the braided conductor of the coaxial cable, requires a sufficient quantity of solder to be deposited within the preformed holes of the printed circuit board for providing maximum signal transfer. Further, a one-handed gun that melts and expels solder is impractical for the very reasons described above.
An example of such a feed apparatus included a welding filler wire feed apparatus comprised of a handpiece, means for advancing filler wire through the handpiece in response to a signal produced by a finger pressure-sensitive switch on the handpiece, and a flexible conduit connecting the handpiece to the filler wire advancing means for passing the filler wire therethrough. The rate of filler wire advancement through the handpiece was adjustable. The mechanism further included wire alignment tubes for directing the filler wire through a pair of idler rollers under spring tension which were driven by the alternating current motor advancing means fed by a transformer through a standard rectifier unit. The finger operated switch activated a relay for energizing the motor while a second switch mounted on the handpiece operated a speed control variable potentiometer.
Another example included an electrical soldering gun incorporating a power cord extending from a pistol grip handle, a slidable trigger for actuating a heat switch and a solder wire feed switch. A central housing enclosed a conventional transformer which was employed for supporting a pair of low resistance electrical conductive elements that terminated in a soldering tip for providing heat sources. A solder wire advancing mechanism was selectively covered by means of a lid rotatively disposed about a hinge to be manually moved between an opened and closed position for readily exposing the solder advancing mechanism.
A further mechanism included a soldering wire feeding mechanism for feeding solder wire from a storage spool which was comprised of a DC motor for driving a feeding wheel for engaging and transporting the soldering wire into a flexible feeding tube. The electrical circuit included a transformer for providing an AC signal to a bridge rectifier circuit for providing direct contact to an electric motor by way of a voltage regulator. In parallel with the motor was a breaking circuit for speed control with the entire circuit controlled by a trigger switch.
In another embodiment, a solder gun included a body and a pistol handle operated by a trigger switch which activated a combination heating element and soldering tip. A transformer enclosed within the body was controlled by a trigger switch for limiting the heat to the solder tip by way of a potentiometer.
Other devices known in the prior art for dispensing solder wire typically include motor driven gear trains for driving a pair of pinch wheels for advancing a line of solder. Some of these devices include more sophisticated electrical control circuits which are driven by alternating current which is rectified and filtered for providing a DC voltage to the field of the solder advancing motor. One of the known circuits includes time delay relays in combination with a potentiometer for controlling the speed of the solder driving motor and further a silicon controlled rectifying circuit for controlling the line voltage to the drive motor.
Hence, those concerned with the development and use of solder dispensing devices in the electronic assembly field have long recognized the need for improved solder dispensing systems which provide means for supporting and expelling solder to a solder joint located on a printed circuit board in which such a solder dispensing device would be capable of maneuvering through a multitude of circuit obstructions. Further, such a dispensing system is necessary to deposit solder at a required location without directly burning the delicate insulation of the signal wire and which permits the completion of the soldering task within a critical time limitation for avoiding heat transfer damage to the delicate coaxial conductor. Further, the soldering device should permit access for soldering joints on both sides of a double sided printed circuit board, should include a geared reduction ratio for providing sensitivity to speed changes and low solder feed rates, and provide a convenient solder replenishing means including convenient access to the drive system of the solder feed device.